2006 E46 325Ci Coolant Leak @ Expansion Tank

[Andrew D]

Hey BMW gang. I signed up to get an answer to the cooling problem I am encountering. I purchased this 2004 BMW 325cI in 2006 and it now has nearly 89,000 miles. For the most part it has been problem free but this one has me puzzled.

For a while the coolant has been seeping from the upper radiator hose connection where it clip connects to the expansion tank. There are two connections there, the smaller diameter one is the culprit. Twice in the past I replaced the upper hose and it temporarily sealed but after a while the leak returned. The second time I used a silicone o-ring lube in the hopes of success.

Yesterday I installed a new expansion tank, reusing the upper hose that is less than 1 year old, and now it is leaking worse than before. I did again use a liberal amount of the silicone o-ring lube. Or should I be using some other type of sealant? I do have some Permatex Anaerobic Gasket Maker in a dark red color that stays soft. I've used it on various paper type gaskets in the past.

These connections click together with the wire clip with no option of tightening. The o-ring should provide the seal, but it is not. The replacement parts I sourced from Rock Auto, they are not genuine BMW parts. Is that my problem?

Have any of you been faced with this? I'm now thinking the solution is a genuine BMW expansion tank and upper hose, but I hate to go through this again without success. Is there a preferred online vendor you recommend?

Thank you in advance for any help you can provide.

[randy72877]

Fcp Euro has lifetime warranty on everything that they sell. They have bmw (oe) and oem (usually same part without the bmw logo) and cheap stuff too. Stick with oe or oem and you should be good. Do yourself a favor and don't buy cheap aftermarket cooling system parts. The long aluminum engine block and head do not tolerate overheating. Trying to save $50 could cost you an engine.

Sent from my S61 using Tapatalk

[randy72877]

I forgot to mention no sealant on the o-rings in the fittings. A little silicone lube is ok to make them slide on easily.

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[Andrew D]

Thank you Randy. I'm now looking on FCP's site for these parts.

Andrew

[MarcoZandrini]

The installation of aftermarket cooling system parts is strictly verboten. The M54 engine is made of aluminum and does not tolerate overheating at all. You need to buy cooling system parts that are labeled “OE” on the FCPEuro website. Is the radiator original? It may be time to replace it. Nissens is the OE brand. Behr will do but they have been known to have fitment issues.

[Andrew D]

The new 16mm o-ring did not seal the leak. So I've now ordered a new expansion tank kit (tank, cap, and other parts) plus new upper and lower hoses from FCPEuro. It will be early next week before they can deliver so the car will have to sit in the garage.
I'll let you know how it turns out.

[jclausen]

Use only factory parts and as a rule replace the lower mounting plate and hardware also its all plastic

[Andrew D]

The parts from FCPEuro delivered Saturday afternoon. Since I already had the old parts removed it didn't take long to reassemble. But before assembly I measured the original expansion tank, the RockAuto tank, and the newly purchased FCP Euro tank. At the port where the hose's o-ring mates all three measured very close to 16.45mm. Considering none of them are cracked all three should be acceptable to use.

Where I did find a difference was the upper radiator hose o-ring connection. The FCP Euro unit's ID measured smaller, as best as I can measure a compressible rubber ID. And it slid onto the expansion tank port requiring more pressure. Side by side comparisons it was obvious the RockAuto upper hose was defective by design and would not seal the expansion tank port.

End result is the cooling system is now sealed properly and I thank you Randy and Marco for your help.

[MarcoZandrini]

You’re welcome! This is the perfect example why I say, “installing aftermarket cooling system parts is strictly verboten.”